Screen grid vacuum tube



P 1933- 'P. E. EDELMAN 1,927,629

SCREEN GRID VACUUM TUBE Filed Nov. 9, 1929 4 Sheets-Sheet 1 Sept. 19, 1933. I p EDELMAN 1,927,629

SCREEN GRID VACUUM TUBE Filed Nov. 9, 1929 4Sheets-She et 2 6 2. ZZ- 5/ i 5/ /Z if p 1933- P. E. EDELMAN I 1,927,629

SCREEN GRID VACUUM TUBE 4 Sheets-Sheet 3 Filed Nov. 9. 1929 Sept. 19, 1933. EDELMAN 1,927,629

SCREEN GRID VACUUM TUBE Filed Nov. 9. 1929 4 Sheets-Sheet 4 Patented Sept. 19, 1933 UNITED STATES SCREEN can) VACUUM TUBE 7 Philip E. Edelman, Chicago, 111., assignor, by mesne assignments, to Robert T. Mack, trustee,

Chicago, 111.

Application November 9, 1929. Serial No. 405,856

' 10 Claims. (Cl. 250-4275) An object of the invention is to provide a vacuum tube of low cost and uniform manufacture having its working elements accurately and permanently aligned, and with structure that withstands rough handling and high temperatures during manufacturing operations.

Various other objects will presently appear, and the novel features combining old elements for the surprisingly improved result are more particularly pointed out in the appended claims.

Heretofore, the manufacture of screen grid type vacuum tubes of uniform quality has been difiicult. During 1929 the rejections of defective vacuum tubes of this class ran as high as 60% in some vacuum tube factories. The difficulties, when analyzed, indicate two major problems, first, the necessity for accurate alignment of the working parts so as to prevent their being easily damaged by rough handling; and second, the necessity for thorough cleaning out of residual gas content from the elements in the evacuated envelope. In the previous practice in the art it has been customary to employ a sealing stem carrying a plurality of wires imbedded in a pinch seal, and to utilize joints to such wires for both mechanical and electrical functions in supporting and leading electrical potential to the vacuum tube elements. While this practice was reasonably successful in the case of three electrode vacuum tube manufacture, it is awkward and inadequate for uniform production of quantities of four electrode alternating current type vacuum tubes.

My invention comprises a departure from current practice in the art, principally in that all of the working elements are first assembled in a rigid accurately aligned structure independent of the sealing stem, or of any wires held by said stem; then the said assembly is sturdily supported by a fastening element attached to said stem, while the electrical connections are made to wires sealed in said stem. No reliance is placed on said stem wires for mechanical support to hold the elements in alignment. By such assembly, mass production and assembly is greatly facilitated with uniform result regardless of the relative differences in positions of the electrical lead-in stem wire. The assembly is also suited to machine operations, after which all of the working elements may be handled as an assembled whole, and have their wire terminals quickly welded to the stem supported lead-in wires without disturbing the relative positions of the working elements.

I am illustrating an exemplification of my invention in the accompanying drawings, in

which- Figure 1 is a front elevation of a partially completed vacuum tube, minus the base and terminal mountings;

Fig. 2 is an enlarged sectioned view on the broken line 2-2 of Fig. 5;

Fig. 3 is an enlarged sectioned view of the oathode structure of Fig. 2;

Fig. 4 is a front elevation of the heater filament 51 and its supports, as shown in Fig. 3;

Fig. 5 is a plan view of one of the insulator discs 11, of Fig. 2;

Fig. 6 is a sectioned side view of a suitable construction for element 38 of Fig. 2;

Fig. 7 is a developed plan view of the structure of Fig. 6;

Fig. 8 shows a developed portion similar to Fig. 7 in modified form;

Fig. 9 shows an end section of the structure shown in Fig. 8; and

Fig. 10 shows a plan view of the completed structure prepared according to Fig. 7.

Referring now to Fig. 1, the embodiment illustrated comprises an evacuated envelope 1 having a sealing stem support 2, provided with a pinch seal portion 2 which carries lead-in wires 2 all in the customary manner, the latter being connected to the usual terminal wires 3, marked for reference purposes respectively-S, for screen grid; F, for heater filament; C, for cathode; P, for plate.

An electrode assembly holder support 7 is provided with a split clamp portion 8 and clamped in place on sealing stem support 2 by a fastener 9. The support 7 may thereby be slipped over the stem 2 and fastened to the stem 2 during manufacture of the vacuum tube. A chemical getter or gas cleaner capsule 10 is suitably carried by the support 7 in a well known manner. The control grid terminal G is sealed at 6 in the cap portion 5 of the envelope 1, and the wire 4 serves as a lead-in wire for this purpose.

All of the electrodes, cathode, grid, screen grid. and plate are combined in an integral or unitary electrode structure 67, adapted to be aligned and held in said structure independently of the sealing wires 2 The structure 67 is carried and supported by the support member 7 and includes two spaced insulator discs 11 and 12 of laminated sheet mica between which, and in and on which the electrode members are supported.

The electrode structure 67 is adapted to be initially and rigidly assembled independently of the stem 2 or sealing wires 2 so that upon completion the structure 67 can be mounted in place and supported by means of the support member '7 as set forth, whereupon connections may be welded to the wires 2 as shown, without disturbing the relative positions of the elements comprising the structure 67. The various elements and dimensions therefor are to be selected of appropriate materials and dimensions in accordance with well known practice in this art.

Inassembling the unit 67, the support member 30 is first inserted through a central opening 23 and is clamped in place on the disc 11, and preferably carries the entire cathode structure C, previously assembled thereon, together with grid G. If desired, the grid G may be assembled on insulator members 28 and 19 after the support 30 is clamped at 30 -to the disc 11.

Next I prefer to mount the inner screen grid supports 60 in and on disc 11. Here too clamping may be omitted, but is preferably done as shown. At this assembly time, the lower supports 60 carry the inner screen grid electrode 38, preferably welded thereto at 44. The bent support portion 60 is laid against the disc 11, while the extension portion 61 passes through perforations therein. and is thereafter bent over or clamped against the disc 11. This may be appropriately accomplished by any customary clamping tool.

A similar operation next mounts the support 24 of the plate P with its clamp portion 2'7 and bent portion 27 on the disc 11. The support 24 carries the plate electrode 39 welded thereto at 26. Thereupon, the outer screen grid electrode member 13, welded to the support at 43 is similarly clamped to the disc 11 by tongue and ear portions 15, 16. At this time, or later on, stem support members 7 may be secured as by spot-welding at 4'7 to the tongues 15. All of the aforesaid assembly operations on the disc 11 may be accomplished simultaneously at one time, if desired, by use of an assembly tool and jig in an obvious manner. A terminal or lead-in wire 36 may be spot-welded to the support 2'7"; also a terminal wire 35 may be spot-welded to the support member 7 to serve as a lead-in wire for the screen grid electrode, S. O.

The top insulator disc 12 prepared with perforations 22, 22*, 22, etc., is next made to engage the upper support members 15*, 61, 25, etc. The cathode bushing cap 20 slides into the central opening inside the disc 12. The supports 61 carried by S. 1., the inner screen grid electrode 38, pass into the perforations 22*. Also, supports 25, carried by plate support members 24 and formed as a part thereof,.pass into perforations 22. The elements 25, 61, respectively, need not be bent over or clamped as in the case of the lower supports previously described.

The terminal wire 4 which is connected to the grid wire 41 may be passed through an opening 22 in the upper disc 12. Thereupon the-support portions 15 16, carried by S.-O., the outer screen grid electrode 13, may be clamped in and on the disc 12. This holds all of the electrode members 38, 39, 40 and cathode C in correct alignment. The screen grid plate shield disc 46 in the form of an annular disc, may now be fastened to 15 and to 61 by spot-welds 45 and 45. If desired, this shield 46 may be omitted and the inner screen grid S. I. will then be connected by a wire 21 which is separately led outside the pinch seal 2 and then connected to the wire S, as shown in Figs. 1 and 2. This enables the inner screen grid S. I. to be separately heated during evacuation according to my application Serial No. 397,250, filed October 4, 1929.

The outer screen grid electrode 40 is preferably made from woven metal screen and fastened to supports 16, 16 by spot-welds 43. The plate ring 39 is preferably made from woven metal screen of closer and thicker mesh than the screen 40,

or may also'be made from sheet metal. The plate electrode 39 is fastened to supports 24, 24 by,

spot-welds 26. S. 1., the inner screen grid electrode, is suitably made from finer wire mesh woven metal 38, and fastened to supports 60 by spot-welds 44. Thin metal sheet may be used for the element 46 which joins S. O. and S. I. electrically.

The cathode and grid assembly principally supported by insulator bushing 28 and cathode cap insulator 19, 20, is held in alignment by the metal ring 29 which is fastened by the support 30 to the disc 11. The grid wire 41 is held in place on the member 28 by the threaded portion 3'7 thereof, and similarly on member 19 by the threaded outer portion thereof. The cathode insulator tube. 18 is held in bushing or hollow insulator 19 at one end and 28 at the other end thereof. The cathode metal sleeve 17 is carried on the cathode tube 18, and has an electron emitting cathode coating portion 42 coated thereon. The bushing 28 also supports the insulating mounting strip 31 provided with terminals 32, 33, and 34. The cathode metal sleeve 17 is connected to the terminal 34 by a lead '56, and the cathode heater filament 51 is connected to terminals 32 and 33, as will later be described.

A refractory insulating tube 18 carries a thin metal sleeve 17 on which electron emitting coating 42 is coated in a customary manner. The coating 42 may comprise oxides or other chemical elements from which electrons may be readily emitted upon heating to a red heat. The tube 18 and its sleeve 17 are mounted in an insulator bushing 28, such as may be made from any suitable material as, for example, a suitable fused silicious compound. The bushing 28 has a neck portion 48 formed therein to accommodate the ring support 29, as shown in Fig. 2. The bushing 48 also has a coned portion 49 and recessed portion 55 adapted to receive and engage with mica insulator support-31.

The cathode insulator cap 19 has a stud portion 20 and fits over the top of the tube 18. It has a perforated portion 20 to accommodate the spring member 53. The mica strip 31 with its terminals 32 and 33 carrying filament wire 51 is adapted to slide in place in the bushing 28, as shown.

Referring now to Fig. 4, the insulating mounting strip 31 carries U-shaped heater filament 51 mounted thereon at 50. The filament'51 is held by a hooked member 52 fastened to a small light spring 53. The spring 53 is attached to an extension wire 54 which is adapted to be threaded through the tube 18 during assembly, and is bent down and cut off to form the support 21 on the cap 20 after the mica strip 31 is locked in alignment and in place in the bushing 28, as shown in Fig. 3. The U-shaped heater wire 51 thus is accurately spaced within and out of contact with the inner wall of the tube 18. The lead-in portions 51 51 of the wire '51 may appropriately be enlarged in section so that it will not heat up to a red heat during use. The metal sleeve 1'7 on the tube 18 has a thin extension 56 which may be fastened to the terminal 34 after the strip 31 is assembled in the bushing 28.

Referring now to Fig. 5, the preferred staggered set forth. an of the electrode members, such as screen grids B. I. and S. 0.. as well as plate P may.

be similarly constructed and assembled, a suitable structure being shown in Figs. 6 and 7, in which the member 8. I is composed of woven wire 38 having supports 60, 61 welded thereto at 44. The wire screen 38 may be of the type known in the trade as Dutch weave, wherein vertical wires 58 are stiiier and further spaced than cross wires 59. The wires 59 may be made from any suitable material, such as molybdenum. The inner screen 38 may be cut to size in developed form which will form a cylinder shaped ring of desired size. The support strips 60, 61 are preferably welded thereto, whereupon portions 60 are bent into position, and the assembled structure appears as shown in the plan view of Fig. 10.

By use of strong mesh screen 64, as in Figs. 8 and 9, I may form the supports 65, 66 integral therewith and therefrom for assembly similar to that of Fig. 10. This modified structure is particularly suitable for low cost construction. when the wire mesh woven screen is used for the membets 8. I., P, and S. 0. respectively, I prefer to use wire screen of different meshes and thicknesses, S. I. having the widest mesh and thinnest wires,

' P having the closest mesh and thickest wires in its structure, and S. 0. having an intermediate mesh and thickness. Also plate P may be of solid thin metal sheet or perforated thick metal foil. Good electron collection qualities will be had by this relative choice of perforation mesh and thickness of material for the elements 3.1., P. and S. 0.

To finish the tube, a socket (not shown) with appropriate prongs is cemented on the bottom, and these prongs connected in a well known manner to the wires 3. Also a metal cap (not shown) is placed over the seal 5 and soldered to the protruding end of the wire 4 in awell known manner. It will be apparent, the outer screen grid S. O. and plate 46 may be omitted, and the support 7 welded to the tongues 2'1 with appropriate changes in the leads 3.

While I have illustrated an embodiment of my invention in an A. C. or heater type screen grid vacuum tube structure, it is obviously suited to other types and classes of thermionic vacuum tubes. such as screen-grid D. C. types, spacecharge grid types, and other multiple-electrode types. Such tubes may be uniformly manufactured in quantities with a very high standard of uniformity and interchangeability.

The electron collection on the screen grid members S. I. and S. 0., during operation thereof, is

relatively small so that it will not be a detriment to the operation of the vacuum tube. The various operations, connections and details, not particularly herein discussed, are to be practiced the same as in the case of other constructions for similar vacuum tubes.

While I have shown and described but a few embodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made which do not depart from the spirit and scope of the invention as disclosed in the appended claims I claim:

1. In a thermionic tube, an envelope having a sealing stem, a plurality of lead-in wires extending through said stem, and a unitary structure supported independently of said lead-in wires, said structure including a cathode and co-operating electrodes, with mica discs having staggered perforations for maintaining said cathode and co-operating electrodes in fixed relation to each other, said cathode and electrodes being. connected to said lead-in wires.-

2. In a thermionictube, an envelope having a sealing stem, a plurality of lead-in wires extending through said stem, and a unitary structure supported on said stem independently of said lead-in wires, said structure including a cathode and co-operating electrodes, and, a plurality of insulator discsprovided with staggered perforations for engaging said electrodes, said cathode and'electrodes being connected to said lead-in wires.

3. In a thermionic tube, an envelope having a sealing stem, a plurality of lead-in wires extending through said stem, and a unitary structure supported independently of said lead-in wires, said structure including a cathode and cooperating electrodes with parallel flat insulators having staggered openings between which are located said cathode and electrodes with the electrodes concentrically disposed around said cathode and having projections engaging a staggered series of openings in said insulators, said cathode and electrodes being connected to said lead-in wires.

4. In a vacuum tube having a plurality of electrode elements, assembly means for mounting said elements in alignment comprising supports for said elements and a plurality of insulating discs having a staggered series of openings formed therein, and some of said supports including clamping means, adapted to engage and hold said supports fastened to said discs.

5. In a vacuum tube having a plurality of electrodes provided with lead-in terminals for said electrodes, assembly means for mounting said electrodes independent from said lead-in terminals comprising a pair of perforated insulating discs and supporting elements for said electrodes held in said discs, said discs having a plurality of series of perforations each series adapted to hold one of said electrodes, the perforations of one series being in' staggered relation to the perforations of the next adjacent series.

6. In a vacuum tube having a cathode, a heater for said cathode, a grid, a screen grid, a p1ate,;a sealing stem, lead-in wires sealed in said sealing stem, and an envelope, a separate assembly supporting means including-discs having a plurality of series of openings therein, each series being in staggered relation to the others for holding said cathode, heater, grid, screen grid and plate independent of said lead-in wires sealed in said stem, and a, fastener for holding said supporting means on said sealing stem.

7. An electrode structure for a screen grid, vacuum tube, comprising a cathode supporting tube, a cathode on said supporting tube, a heater element in said supporting tube, a supporting cap engaging one end of said cathode supporting tube, a combined cap and grid support held on the other end of said cathode supporting tube, a grid mounted on said last named support, a plurality of co-operating electrodes spaced from said cathode, supports for said last named electrodes, an insulator disc holding said supports, and a perforation in said disc to engage said cathode tube supporting cap whereby said cathode is held in alignment with respect to said co-operating electrodes.

8. A structure for the cathode of a vacuum tube consisting of a U-shaped heater wire, an insulator support for said wire, terminals carried by said insulator support, an insulator bushing iormed to engage said insulator support, a cathode insulator mounted in said bushing,. a metal sleeve carried by said cathode insulator, a surface capable of emitting electrons when heated coated on said metal sleeve, and a cathode cap insulator formed to engage one end of said metal sleeve on said cathode insulator.

9. An electrode structure for a screen grid vacuum tube, comprisinga cathode, a grid supported in spaced relation about said cathode, a pair of discs carrying said cathode, a screen grid supported between said discs and spaced from said grid, an anode carried by said discs and provided with a plurality of staggered per1orations,'a plurality of electrode elements adapted to engage said perforations and held on the disc, and means to support the disc within the vacuum tube.

. PHILIP E. EDELMAN. 

